Though citizens of those nations do not need visas to enter the United States for as long as 90 days, their admission is up to the discretion of border agents. There are more than 60 grounds for finding someone inadmissible, including a hunch that the person plans to work or immigrate, or evidence of an overstay, however brief, on an earlier visit.

While those turned away are generally sent home on the next flight, “there are occasional circumstances which require further detention to review their cases,” Ms. De Cima said. And because such “arriving aliens” are not considered to be in the United States at all, even if they are in custody, they have none of the legal rights that even illegal immigrants can claim.

[…]

Ms. Cooper said that at the airport, when she begged to know what was happening to Mr. Salerno, an agent told her, “You know, he should try spending a little more time in his own country.”

Another agent eventually told her to go home because Mr. Salerno was being detained as an asylum-seeker.

[…]

Ten days after he landed in Washington, Mr. Salerno was still incarcerated, despite efforts by Senator John W. Warner, Republican of Virginia, and two former immigration prosecutors hired by the Coopers.

[…]

Luis Paoli, a lawyer hired by the Coopers, said there was no limit on detention while waiting for an asylum interview. But even after officials agreed the asylum issue had been a mistake, Mr. Salerno was not released.